Windmills have been used for many generations for the purpose of pumping water from the ground and for generating electricity. A basic advantage of the windmill is that it uses the power of atmospheric wind to rotate a wheel having radially extending blades. This rotary movement may be converted into various useful purposes. For example, wind turbines in the form of propellers mounted on towers have been placed in areas where steady winds are prevalent and the wind turbines are used to generate electricity.
The blades of the conventional wind turbines are very large and made of expensive rigid material and are constructed to have the blades extend radially from a central hub, with no extra support at the outer tips of the blades. The conventional wind turbine blades rotate at a high rate of revolutions and must withstand both the centrifugal forces generated by the fast revolution of the blades and the cantilever bending forces applied to the blades by the wind. Since the outer portions of the blades move at a very high velocity and are engaged by strong winds, the larger the blades the stronger they must be and the more expensive they become. Thus, there is a practical limit as to the length and width of the blades.
Another type of wind turbine is one that has sail wings constructed of fabric that are a substitute for the rigid blades of the conventional wind turbines described above. For example U.S. Pat. Nos. 4,330,714, 4,350,895, and 4,729,716 disclose wind turbines that use cloth “sails” that catch the wind. The blades of the wind turbine are formed of lighter weight material.
Another wind turbine type has rigid propellers that appear to be rigidly mounted to circular perimeter rims that support the outer ends of the propellers, as shown in U.S. Pat. Nos. 1,233,232 and 6,064,123.
Some of the wind turbines of the patents cited above are constructed with an outer rim that extends circumferentially about the turbine wheel. Rubber tires or other rotary objects are placed in positions to engage the outer rim so as to rotate the rubber tires, with the driven tires rotating the rotor of a generator. Thus, the rotation of the wind turbine is used to generate electricity.
Some of the prior art wind turbines as described above control the rate of rotation of the turbine wheel by turning the turbine wheel at angles with respect to the oncoming wind. Typically, the generators have an optimum speed range in which they operate, requiring the turbine wheel to rotate within a range of revolutions per unit of time. Also, the driving of a generator involves the application of rotary motion to the rotor of the generator and overcoming the drag and frictional forces required to operate the generator.
While wind turbines have found use in open land areas where steady winds are prevalent, the land areas most suitable for catching the wind on wind turbine propeller blades usually are remote from the areas of great need of electrical power. Therefore, there is a requirement that electrical power be transmitted through conductive cables for long distances to the areas of need.
Winds generated over large bodies of water, particularly over an ocean, are not confronted with mountains, buildings, and the vegetation of the land masses that tend to slow the velocity of winds. Also, some of the largest cities of the world are positioned adjacent large bodies of water such as oceans and seas where wind velocities are not slowed near the water surface and are high and predictable. Accordingly, it would be desirable to locate wind turbines on bodies of water spaced relatively close to a land mass where there is a need for electricity. However, the supports for wind turbines usually are connected to the ground surface so that the stability of the wind turbines may be maintained. However, the expense of mounting wind turbines to the bottom of an ocean or other large body of water is expensive and usually is not practical from an engineering standpoint.